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Fetch specific field values in MongoDB
To fetch specific field values, use $in operator. The $in selects the documents where the value of a field equals any value in the specified array.
Let us first create a collection with documents −
> db.indexesDemo.createIndex({"StudentFirstName":1});
{
"createdCollectionAutomatically" : true,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}
> db.indexesDemo.insertOne({"StudentFirstName":"John","StudentLastName":"Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e06de4d25ddae1f53b621dd")
}
> db.indexesDemo.insertOne({"StudentFirstName":"Chris","StudentLastName":"Brown"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e06de5825ddae1f53b621de")
}
> db.indexesDemo.insertOne({"StudentFirstName":"John","StudentLastName":"Doe"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e06de6725ddae1f53b621df")
}
> db.indexesDemo.insertOne({"StudentFirstName":"David","StudentLastName":"Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e06de7225ddae1f53b621e0")
}Following is the query to display all documents from a collection with the help of find() method −
> db.indexesDemo.find();
This will produce the following output −
{ "_id" : ObjectId("5e06de4d25ddae1f53b621dd"), "StudentFirstName" : "John", "StudentLastName" : "Smith" }
{ "_id" : ObjectId("5e06de5825ddae1f53b621de"), "StudentFirstName" : "Chris", "StudentLastName" : "Brown" }
{ "_id" : ObjectId("5e06de6725ddae1f53b621df"), "StudentFirstName" : "John", "StudentLastName" : "Doe" }
{ "_id" : ObjectId("5e06de7225ddae1f53b621e0"), "StudentFirstName" : "David", "StudentLastName" : "Miller" }Following is the query to indexes −
> db.indexesDemo.find(
... { StudentFirstName: { $in: [ "John", "David" ] } },
... { _id: 0, StudentLastName: 0 }
... );This will produce the following output −
{ "StudentFirstName" : "David" }
{ "StudentFirstName" : "John" }
{ "StudentFirstName" : "John" }
Updated on: 31-Mar-2020
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